The present invention relates to a method and apparatus for the graphic, particularly photographic, registration of moving vehicles by a Doppler radar speed measuring device equipped with a recording device such as a camera.
More particularly, the present invention combines a Doppler radar speed measuring device with a recording device so that a proper record can be made of cars which exceed the applicable speed limit. After a vehicle enters the measuring beam of the radar device, the vehicle is registered from the direction in which it is travelling and a corresponding measured speed value is determined during a measuring stage. If the measured speed value exceeds a specific threshold value, the recording device is triggered and the measured speed value is printed or superimposed onto the photograph.
German Patent No. 1 805 903 (U.S. Pat. No. 3,754,253) discloses a process for triggering a camera with a Doppler radar speed measuring device, in which the vehicles are measured from behind and photographed. The triggering of the camera is suppressed when the measured speed value cannot be assigned with certainty to a particular vehicle.
Since when surveying and photographing moving traffic from behind a vehicle only the vehicle at fault is identified and not the driver thereof, the practice has recently been adopted of taking a so-called frontal photograph either with or without the photograph from behind, which also makes possible a clear identification of the driver of the vehicle. A suitable device is disclosed, for example in German patent No. 28 02 448.
Thus, either a speed measuring device of the type described in German Patent No. 1 805 903 (U.S. Pat. No. 3,754,253) is positioned at the roadside together with a frontal camera device such as the type described in German Patent No. 28 02 448 coupled to it and the vehicles are measured from behind and photographed both from behind the vehicle and from the front, or a single speed measuring device is used and the vehicles are measured and photographed only from the front.
In the first case, the apparatus becomes more expensive due to the use of two cameras and it also becomes impractical and is only suitable for stationary and not for mobile use. In the second case, the requirement that the vehicle must be photographed as soon as possible after entering the measuring area of the radar device, since otherwise it will leave the field of vision of the camera, means that the determination of the speed value must take place within a relatively short measuring distance. Since the measurement is immediately concluded after the determination of the measuring value, the camera is triggered while the vehicle is still at the beginning of the measuring range of the radar device. Thus, the greater part of the Doppler signal produced as the vehicle travels through the measuring beam remains unevaluated, thereby reducing the measuring reliability.
Thus, for example, a vehicle passing another directly during or after the measurement within the measuring range of the radar device is not detected, since several vehicles are shown on the corresponding photograph in a relatively small area, and the certain allocation of the printed measured speed value to one particular vehicle shown is not possible. So as to avoid incorrect allocation, the evaluation of such photographs having several vehicles at relatively small spacings must be dispensed with. The proportion of those photographs which cannot be evaluated, however, is relatively large in today's heavy traffic.